Even using the small size adjuster, your headband can feel a little bit lose, or even move during the night.
Here are a couple of tips that can help you if you are in that case:
1. Open up the small spacer. Pull each side of the elastic band as far as it will go across to the other side, ignoring the round sticky pads. Put the piece going over it back in place. This will make your headband a lot tighter.